Space is often limited for vehicle-mounted equipment boxes containing electronic equipment. To efficiently use the available space, the vehicle-mounted equipment boxes are frequently designed to fit within a small area with very little clearance between the equipment boxes being mounted and other equipment boxes in the surrounding space. The close proximity of equipment boxes makes it difficult to access and securely tighten fasteners to secure the equipment boxes. One way of mounting the equipment boxes in a small area with very little clearance is using dagger pins that are typically mounted in the bottom or least accessible portion of the equipment box mounting area.
The equipment boxes also typically require an electrical bonding path for grounding the equipment box. Frequently, the dagger pin has been used to provide the electrical bonding path for grounding the equipment box. However, while dagger pins are effective for securing equipment boxes in vehicles, dagger pins do not provide a reliable electrical bonding path due to interface tolerances necessary to permit equipment box alignment and installation on the dagger pins. Since both non-spring loaded mounting dagger pins and spring loaded mounting dagger pins rely on direct surface-to-surface physical contact between the dagger pin and contact plate to form the electrical bonding path, the resulting electrical bonding path is frequently intermittent even under non-vibration environment conditions. This results in an ineffective Electrical Magnetic Interference/Electrical Magnetic Compatibility (EMI/EMC) shielding of the equipment box, which can cause unstable operation of the electronics in the equipment box.
Further, the electrical resistance of the ground path provided by existing dagger pins is typically significantly greater than 2.5 milli-ohms, which is the desired upper limit. Vibrations that may be present during operation in a vehicle environment exacerbate the intermittent electrical bonding path problem.
Prior attempts to solve this problem have included using electrically conductive spring fingers, non-painted contact surfaces and bonding straps. The electrically conductive spring fingers are not effective because the electrically conductive spring fingers can lose resiliency and can break without warning, particularly under the vibration conditions present during operation in a vehicle, in addition, using electrically conductive spring fingers requires retrofit of existing electronics boxes with hard conductive pads positioned to interface with the electrically conductive spring fingers. Using non-painted contact surfaces is also not desirable because they cause the bare surfaces of the equipment box and bare portions of the mounting structure to be much less corrosion resistant and more subject to wear, and surface corrosion on these surfaces causes intermittent loss of bonding, especially under vibration and load conditions. Bonding straps also are not desirable because these add additional hardware and requires modification of the equipment boxes and the vehicle mounting structure, and add additional steps for the removal and installation of the equipment boxes, which is not desirable.
What is needed is a system and method for providing a reliable electrical bonding path for equipment boxes under non-vibratory and vibratory conditions to ensure proper operation of electronic equipment contained in vehicle-mounted equipment boxes without major modification to the equipment boxes or the vehicle mounting structure.